Ashura day in Iran
And so it came the day of Ashura, which is a very special day in Iran. The tradition of mourning for Imam Hossein has deep roots among Iranian people, not necessarily the Muslim ones:
"Lamentation for the death of mythological heroes was popular before Islam also in Iran. In his History of Bokhara, Narshakhi says: "The people in Bokhara sung strange songs to lament Siavosh's death and the minstrels called these songs `The Wrath of Siavosh". The people in Bokhara lament Siavosh's murder and this custom was popular in all provinces and minstrels composed songs and singers chanted doleful lays and wept..."
Ashura ceremony and the story of Imam Hossein is a manifestation of highly oppressed and devalued ambitions and values of people. People love dignity, freedom and honesty and they find their extreme manifestation in the story of Ashura. The ceremony of Ashura has been oppressed by many closed political regimes during the contemporary history of the world, because of its huge socio-political potential, which may have led to severe resistance and protests.
And read some more from wikipedia about Ashura:
The Day of Ashura (عاشوراء translit: ‘Āshūrā’, also Aashoora and other spellings) is on the 10th day of Muharram in the Islamic calendar and marks the climax of the Remembrance of Muharram but not the Islamic month.
This day is well-known because of mourning for the martyrdom of Husayn ibn Ali, the grandson of Muhammad at the Battle of Karbala in the year 61 AH (AD 680).
This day is of particular significance to Shi'a Muslims, who consider Husayn the third Imam and a rightful successor of Prophet Muhammad a.s. Many Shi'a make pilgrimages on Ashura to the Mashhad al-Husayn, the shrine in Karbala, Iraq that is traditionally held to be Husayn's tomb. Shi'as also express mourning by thumping their chests and crying after listening to Speeches on How Hussain and his family were Martyred. This is intended to connect them with Husayn's suffering and death. Husayn's martyrdom is widely interpreted by Shi'a as a symbol of the struggle against injustice, tyranny, and oppression.